Techniques (pattern-forming techniques) in which a fine pattern is formed on top of a support, and a lower layer beneath that pattern is then fabricated by conducting etching with this pattern as a mask are widely used in the semiconductor industry for IC device fabrication and the like.
These types of fine patterns are usually formed from an organic material, and are formed, for example, using a lithography method or a nanoimprint method or the like. In lithography techniques, for example, a resist film composed of a resist material is formed on a support such as a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. Using this resist pattern as a mask, a semiconductor or the like is produced by conducting a step in which the substrate is processed by etching.
Resist materials in which the exposed portions exhibit increased solubility in a developing solution is called a positive type, and a resist material in which the exposed portions exhibit decreased solubility in a developing solution is called a negative type.
In recent years, advances in lithography techniques have led to rapid progress in the field of pattern miniaturization. Typically, these miniaturization techniques of a resist pattern involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production of the semiconductor elements. For example, by lithography using ArF excimer laser, a pattern having a resolution of 45 nm level is formed. Furthermore, in order to enhance resolution, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter than these excimer lasers, such as F2 excimer lasers, electron beam, extreme ultraviolet radiation (EUV), and X ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources. As a resist material that satisfies these conditions, a chemically amplified composition is used which includes an acid generator that generates acid upon exposure. In a chemically amplified resist composition, a base component which exhibits changed solubility in a developing solution under action of acid is generally used in addition to the acid generator. For example, in a chemically amplified positive resist composition, a base component which exhibits increased solubility in an alkali developing solution under action of acid is used. Conventionally, a resin is typically used as the base component of a chemically amplified resist composition (see Patent Document 1).
As a technique for further improving the resolution, a lithography method called liquid immersion lithography (hereafter, frequently referred to as “immersion exposure”) is known in which exposure (immersion exposure) is conducted in a state where the region between the lens and the resist layer formed on a wafer is filled with a solvent (an immersion medium) that has a larger refractive index than the refractive index of air (see for example, Non-Patent Document 1).
According to this type of immersion exposure, it is considered that higher resolutions equivalent to those obtained using a shorter wavelength light source or a larger NA lens can be obtained using the same exposure light source wavelength, with no lowering of the depth of focus. Furthermore, immersion exposure can be conducted by applying a conventional exposure apparatus. As a result, it is expected that immersion exposure will enable the formation of resist patterns of higher resolution and superior depth of focus at lower costs. Accordingly, in the production of semiconductor devices, which requires enormous capital investment, immersion exposure is attracting considerable attention as a method that offers significant potential to the semiconductor industry, both in terms of cost and in terms of lithography properties such as resolution.
Immersion lithography is effective in forming patterns having various shapes. Further, immersion exposure is expected to be capable of being used in combination with currently studied super-resolution techniques, such as phase shift method and modified illumination method. Currently, as the immersion exposure technique, technique using an ArF excimer laser as an exposure source is being actively studied. Further, water is mainly used as the immersion medium.
As a lithography technique which has been recently proposed, a double patterning method is known in which patterning is conducted two or more times to form a resist pattern (for example, see Non-Patent Documents 2 and 3).
There are several different types of double patterning process, for example, (1) a method in which a lithography step (from application of resist compositions to exposure and developing) and an etching step are performed twice or more to form a pattern and (2) a method in which the lithography step is successively performed twice or more.
Formation of patterns according to the step (1) can be conducted, for example, by the following procedure. A laminate is prepared in which a substrate, a lower-layer film and a hard mask are laminated. Subsequently, a resist film is formed on the hard mask, and the resist film is subjected to selective exposure and developing through a photomask, thereby forming a first resist pattern in which a plurality of hole patterns having a predetermined size are arranged at predetermined positions. Then, the hard mask is subjected to etching by using the first resist pattern as a mask, followed by the removal of the remaining first resist pattern. As a result, a hard mask is obtained in which the image of the first resist pattern is transferred. Subsequently, a resist composition is applied to the hard mask. As a result, a resist film is formed which fills in the concave portions within the hard mask. Then, the resist film is subjected to selective exposure through some photomask having a different pattern arranged, followed by developing to form a second resist pattern. Then, the hard mask is subjected to etching by using the second resist pattern as a mask, followed by the removal of the remaining second resist pattern. As a result, a hard mask is obtained in which the image of the first resist pattern and the image of the second resist pattern are transferred. The image of the pattern of the hard mask is transferred to the lower-layer film by conducting an etching process using the hard mask as a mask. As a result, a pattern is formed, which has a narrower pitch than that of photomask used.
According to the method (2), for example, a first resist film is formed on a substrate, and patterning of the first resist film is conducted to form a plurality of resist patterns (first resist pattern). Then, a second resist material is applied to the plurality of resist patterns to form a second resist film which fills in the concave portions between the plurality of resist patterns. Then, patterning of the second resist film is conducted.
According to the double patterning method, a resist pattern with a higher level of resolution can be formed, as compared to the case where a resist pattern is formed by a single lithography step (namely, a single patterning process), even when a light source with the same exposure wavelength is used, or even when the same resist composition is used. Furthermore, double patterning process can be conducted using a conventional exposure apparatus.
As a lithography technique which has been recently proposed, a pattern formation method by which the image of a positive pattern is reversed to a negative pattern has been proposed (see Patent Document 2). The method includes: a step in which a positive pattern is formed using a chemically amplified positive composition containing: a resin which contains a repeating unit having an acid labile group capable of being removed by acid and which exhibits solubility in alkali developing solution after removal of acid labile group, an photo acid generator that generates acid upon exposure of high-energy radiation or a heat acid generator that generates acid by heating, and an organic solvent; a step in which the obtained positive pattern is exposed or heated so as to increase alkali solubility thereof due to removal of acid labile group in the resin of the positive pattern by the action of acid or heat, and form a crosslink thereby ensuring resistance to an organic solvent, such that the solubility of the resin in alkali wet etching solution is not impaired; a step in which a reversing film is formed using a composition for forming a pattern reversing film; and a step in which the positive pattern having the crosslink formed is dissolved and removed using an alkali wet etching solution.